This invention relates generally to wheels for use to move work machines about the ground and more particularly to a geometric design for a wheel.
Work machines, such as off-highway trucks and wheel loaders, typically have at least a pair of wheels that are rotatably mounted on corresponding axles or spindles. The wheels, when assembled on the work machine, may additionally attach to wet (liquid cooled) brake assemblies and have a rim and tire mounted to the wheel. Such wheels have a hub that defines a cavity for reserving a quantity of bearing lubricant, and a first seal arrangement serves to contain the lubricating oil in the hub. A second sealing arrangement serves to contain the brake coolant in the brake at the position where the non-rotatable portion of the brake interfaces with the rotatable wheel. There are two basic types of forces or loads exerted on the structure of the wheel. The first is an axial force caused by the pre-loading of the wheel bearings. To maximize the life of the wheel bearings, axial should be maintained nearest to the specifications of the bearing manufacturer as possible. Second is a radial force caused by the weight of the machine on each wheel. The radial forces on the wheel tend to be more dynamic and fluctuate greatly due to machine traveling across rough or uneven terrain. Because the rim mounting flange extends from the hub, the radial forces are translated to the hub. Additionally, the positioning of the wheel bearings in relation to the centerline of the load, also referred to as a load line, has a large impact on bearing life. This is particularly true for steerable wheels. For example, if one of the bearings on a steerable wheel is axially positioned near the load line of the wheel, there are higher twisting forces on the bearing than if the same bearing is positioned farther away from the load line.
The geometric design of the wheel may additionally impact the life and functionality of the seals. It is most desirable to have a geometric design including a hub that is substantially cylindrical cross section between the wheel bearings with the rim mounting flange extending outward perpendicular to the hub. The cylindrical hub design translates pre-load forces through the hub primarily through axial force vectors and the radial forces are translated perpendicular to the axial forces. A hub having an oval or angled cross section translates the pre-load and radial forces through a greater combination of axial and radial force vectors, this results in a coupling of the independent pre-load and radial forces. The coupling of the independent forces now causes the critical pre-load become dynamically impacted. As with the design of many structures, the typical design of a wheel permits a predetermined amount of elastic deformation or flexing. It is desirable to permit some flexing of the rim mounting flange in order to minimize flexing near critical elements, such as, sealing surfaces and bearing mounting surfaces.
An additional problem with work machines of this nature is that road conditions at many mine sites throughout the world are extremely bad. Many of the roads are typically constructed of dirt and rocks. Small rocks and debris gets picked up by the tires and may be dropped into the wheels, the rocks and debris may accumulate near seal cavities. Additionally, water is often spayed on the roads to reduce dust. The dirt is therefor turned to mud, and the mud is thrown onto the wheel. A build of debris, mud and rocks near the wheel seals may open or cause damage to the seals. A damaged seal may in turn cause a loss/or contamination of brake coolant or bearing lubrication, resulting in premature mechanical failure of associated components.
The present invention is directed to overcome one or more of the problems described above.
In one aspect of the present invention, a rotatable wheel for a work machine has a central axis and a cylindrical hub defined about the axis. The hub has an inside surface and an outside surface outwardly spaced from the inside surface. Additionally, the hub has an inboard end and an outboard end opposite the inboard end. Bearing mounting surfaces are located on the inside surface of the hub near the inboard and outboard ends. A first sealing surface is located near the inboard end and adjacent the hub""s inner surface. The rotatable wheel comprises a rim mounting flange extending radially outward from the outside surface interposed the inboard and outboard ends, a second sealing surface extends about the hubs outside surface and a recessed portion is located on the outside surface between the mounting flange and the second sealing surface. The recessed portion provides a barrier to keep debris away from the second sealing surface.
In a second aspect of the present invention, is provided a work machine having a plurality of rotatable wheels. The rotatable wheels are adapted for moving the work machine along a surface. Additionally, the work machine has a engine and a drive train. At least one of the rotatable wheels is connected to the drive train. At least one of the rotatable wheels comprises a cylindrical hub with central axis and an inside surface defined about the central axis. An outside surface is spaced outward of the inside surface. An inboard end is defined on the hub and an outboard end is spaced axially away from the inboard end. A bearing mounting surface is located on the inside surface near each of the inboard and outboard ends. A mounting flange extends radially outward from the outside surface. A first sealing surface is positioned inboard and adjacent to the inboard bearing surface. A second sealing surface is positioned between the mounting flange and the inboard end. A recessed portion of the hub is positioned between the mounting flange and the second sealing surface.